Although many attempts have been made for life extension, the possibility of scientific life extension has been found only recently.
Caloric restriction has heretofore been known as a method for causing life extension regardless of organism species. The caloric restriction prolongs average life and/or maximum life in a wide range of different organisms including yeasts, Trochelminthes, guppies, spiders, fruit-flies, hamsters, rats, and mice. In this context, the “caloric restriction” refers to the restriction of the total number of calories derived from carbohydrates, lipids, and/or proteins to a level that is 25% to 60% lower than the calories of freely fed control animals.
In addition, the caloric restriction also delays the development of aging-related diseases and thereby offers healthier life for a longer period, in addition to the prolonging of life. For example, the caloric restriction is known to delay the development of kidney diseases, autoimmune diseases, and diabetes mellitus in mammals.
Furthermore, the caloric restriction reduces even aging-related neuron loss in mouse models of Parkinson's disease and Alzheimer's disease. The caloric restriction has also been found to reduce a risk of cancer in mammals and to enhance DNA repair in the skin and other tissues after exposure to ultraviolet rays.
Such action of the caloric restriction on a wide range of organisms from unicellular organisms to very complicated organisms (including primates) is important from the viewpoint that the process of prolonging life is conserved across species. The rate of prolonging of life can reach 50% in rodents. However, calories necessary for organisms are usually at least 25% smaller than their consumed calories. Therefore, this prolonged life is obtained from considerable sacrifice such as hunger or limitation of activity (Patent Literature 1).
As another method, it is also possible to extend life by gene manipulation. However, the gene manipulation is not considered to be sufficiently safe and furthermore, cannot be readily applied.
Substances extending life have been found as a method for overcoming these disadvantages. For example, resveratrol, a polyphenol contained in grape skins, is known to be effective for mice fed with high-fat diet. In this process, sirtuin genes are reportedly activated.
Metformin, a therapeutic drug for diabetes mellitus, also has a life-extending effect. This drug is considered to increase the level of AMP-activated protein kinase. Also, rapamycin having an immunosuppressive effect has a life-extending effect. However, these drugs are expensive and might also cause adverse reactions by administration. Thus, there has been a demand for a substance that is inexpensive and has no adverse reaction (Non Patent Literatures 1 and 2).